A metal foil strain gauge, which is provided with a metal resistor (metal foil) on a thin insulator, has been well known from a long time ago as a device to measure deformation (strain) of a measurement target object. The metal foil strain gauge is configured to measure a change of an electrical resistance value according to deformation of the metal foil, which depends on deformation of the measurement target object, and to convert the measured value into the amount of strain and is highly accurate despite its simple structure and low price, and thus, has been widely used. Meanwhile, the metal foil strain gauge has weak points in terms of its configuration such as a point that a measurement error is likely to occur if temperature of an object to be measured is changed, a point that power consumption is too great to constantly drive the gauge, and a point that a certain extent of installation area is required.
A semiconductor strain sensor, which is provided with a strain detection region (bridge circuit) configured using an impurity diffusion resistor formed on a surface of a semiconductor substrate, has been developed as a device to overcome those weak points of the metal foil strain gauge. In the semiconductor strain sensor, a resistance change rate of the impurity diffusion resistor in relation to strain is as large as several tens of times that of the metal resistor of the conventional metal foil strain gauge, and thus, can detect even minute strain (that is, there is an advantage that the sensitivity with respect to strain is high). In addition, the impurity diffusion resistor can have finer pattern by employing a so-called semiconductor process such as photolithography for formation of the impurity diffusion resistor, and it is possible to miniaturize (reduce the area of) the entire semiconductor strain sensor and to obtain power saving. Further, it is possible to form all resistors, which form Wheatstone bridge circuit, on the same substrate through the finer pattern of the impurity diffusion resistor, and thus, there is also an advantage that a variation of electrical resistance in relation to the change in temperature of the object to be measured is offset, and the measurement error decreases (the measurement accuracy is improved).
For example, Japanese Patent Application Laid-open No. 2007-263781 (PTL 1) describes a mechanical quantity measuring device that is provided with a strain detection unit on a surface of a semiconductor substrate and is adhered to a measuring object to measure strain. In this mechanical quantity measuring device, at least two or more sets of bridge circuits are formed on a semiconductor monocrystalline substrate. One bridge circuit among the two sets of bridge circuits is configured using an n-type diffusion resistor in which a direction of causing electric current to flow and measuring a variation of a resistance value (longitudinal direction) is parallel with a direction <100> of the semiconductor monocrystalline substrate. Another bridge circuit is configured in combination with a p-type diffusion resistor in which a longitudinal direction is parallel with a direction <110>. According to PTL 1, it is possible to measure a strain component generated in the measuring object in a specific direction with high precision (see Abstract).